Non-contact fluid characterization in containers using ultrasonic waves

Abstract

Apparatus and method for non-contact (stand-off) ultrasonic determination of certain characteristics of fluids in containers or pipes are described. A combination of swept frequency acoustic interferometry (SFAI), wide-bandwidth, air-coupled acoustic transducers, narrowband frequency data acquisition, and data conversion from the frequency domain to the time domain, if required, permits meaningful information to be extracted from such fluids.

1. An apparatus for non-contact characterization of a fluid in a container or a pipe, said container or said pipe having a wall having an outer surface, comprising in combination:
 an air-coupled transmitting transducer disposed outside of said container or said pipe for generating ultrasonic waves approximately perpendicular to the outer surface of the wall at a chosen first distance therefrom; 
 a sweep generator for exciting said air-coupled transmitting transducer at chosen frequencies in a selected frequency range, whereby resonant vibrations are generated in the fluid; 
 an air-coupled receiving transducer disposed in any configuration on the other side of said container or said pipe from said transmitting transducer at a second chosen distance from the outer surface of the wall, for receiving said resonant vibrations emitted by said fluid and perpendicular to the outer surface of the wall, said receiving transducer producing an electrical signal in response to the ultrasonic waves received thereby; 
 a narrow-band tracking filter for receiving the electrical signal from said receiving transducer at the chosen frequencies in the selected frequency range and for generating a noise-filtered signal therefrom; 
 a signal processor for receiving the noise-filtered signal from said narrow-band tracking filter and producing a signal containing simultaneous amplitude and phase information from the ultrasonic waves in the frequency domain; and 
 circuitry for receiving the signal from said signal processor in the frequency domain and transforming the signal into the time domain by Fast Fourier Transform. 
 
     
     
       2. The non-contact characterization apparatus of  claim 1 , wherein the selected frequency range is between 0.4 and 1400 kHz. 
     
     
       3. The non-contact characterization apparatus of  claim 1 , wherein the first chosen distance from an inner surface of the wall of said container or said pipe, and the second chosen distance from the inner surface of the wall of said container or said pipe, are greater than 1 cm. 
     
     
       4. The non-contact characterization apparatus of  claim 1 , wherein the outer surface has two parallel walls, said transmitting transducer being perpendicular to one of the parallel walls and said receiving transducer being perpendicular to the other of the parallel walls. 
     
     
       5. A method for non-contact characterization of a fluid in a container or a pipe, the container or pipe having a wall with an outer surface, comprising the steps of:
 generating ultrasonic waves having a chosen frequency in a selected frequency range approximately perpendicular to the outer surface of the wall from a first chosen distance therefrom, whereby resonant ultrasonic vibrations are generated in said fluid; 
 sweeping the generated ultrasonic waves over the selected frequency range to obtain simultaneous amplitude and phase measurements; 
 detecting the resonant ultrasonic vibrations emitted perpendicular to the outer surface of the wall of the container or the pipe at a second chosen distance therefrom; 
 producing a signal from the detected ultrasonic vibrations; 
 generating a narrow-band, noise-filtered signal at each frequency from the signal; whereby a signal containing amplitude and phase information from the resonant ultrasonic vibrations is generated in the frequency domain; and transforming the signal containing amplitude and phase information into the time domain by Fast Fourier Transform. 
 
     
     
       6. The non-contact characterization method of  claim 5 , wherein the selected frequency range is between 400 and 1400 kHz. 
     
     
       7. The non-contact characterization method of  claim 5 , wherein the first chosen distance from the surface of said container or said pipe and the second chosen distance from the surface of said container or said pipe, are greater than 1 cm. 
     
     
       8. The non-contact characterization method of  claim 5 , wherein said step of generating ultrasonic waves having a chosen frequency is achieved using an air-coupled transmitting transducer disposed outside of the container or the pipe and excited by a sweep generator, and said step of detecting ultrasonic waves emitted by the fluid is achieved using an air-coupled receiving transducer disposed outside of the container or the pipe on the opposite side of the container or the pipe from the transmitting transducer. 
     
     
       9. The non-contact characterization method of  claim 8 , wherein the outer surface has two parallel walls, the transmitting transducer being perpendicular to one of the parallel walls and the receiving transducer being perpendicular to the other of the parallel walls.